The present invention relates to reactive ion etch (RIE) systems. More particularly, the invention relates to a RIE chamber wafer masking system, wherein a mechanical mask facilitates the implementation of multiple etches on a single semiconductor wafer.
Devices fabricated on semiconductor wafers are becoming increasingly complex, as are the tools and processing steps employed in building those devices. The cost of processing a single semiconductor wafer is likewise continually increasing. Accordingly, there is an ongoing need for innovative tooling solutions in order to control processing costs wherever possible.
In the development and control of RIE processes, it is common to etch patterns under several different conditions in order to define the limits of a specific process or process capability. Testing of a RIE process for production requires that a wafer be etched under conditions as close as possible to those in an actual production tool. This often requires that one entire wafer be etched at a particular set of conditions. Determining the optimum process with this approach may require a large number of wafers, which are not only expensive, but at times may be impractical or even impossible to procure. Consequently, any reduction in the quantity of wafers employed will result in considerable cost savings.
Workers in RIE process development have used a technique of mechanically masking a portion of a wafer during an etch process test, thereby preserving the masked area of the wafer for use in a subsequent test. This technique permits a single test wafer to be used in multiple etching conditions, so that fewer wafers need be used for process testing. However, the use of mechanical masks has not been extensive, inasmuch as the mask surface composition ordinarily does not match that of the semiconductor wafer surface; this causes the etching plasma to be unstable and not representative of the plasma during actual production. In addition, placing a mechanical mask directly on the wafer to be etched may damage the wafer surface.
Accordingly, it is desirable to provide a shielding or masking platter for a semiconductor wafer which permits localized etching of the wafer in order to provide for multiple etches at different locations (thereby resulting in the saving of wafers), while allowing a stable plasma which mimics the conditions in the production RIE process.
The shielding or masking of all or at least a portion of the surface of semiconductor wafers during processing or etching thereof has long been utilized in industry. In particular, lithographic processes related to RIE are well known, wherein a masking material deposited on a wafer has patterns formed therein to shield regions of the semiconductor wafer surface from the RIE plasma.
Reactive ion etching (RIE) of semiconductor wafers or chips has been employed for a considerable number of years. For example, Muto (U.S. Pat. No. 3,971,684) describes a RIE chamber utilized for etching thin film circuits on a substrate, wherein the substrates to be etched are covered by masks and positioned on a cathode electrode which is enclosed in the chamber. The chamber also contains a chemically reactive gas employed as an etchant; the cathode is negatively biased so as to ionize the reactive gas and attract the chemically reactive ions toward the cathode. However, the disclosure in Muto does not contemplate the use of a mechanical mask which will enable multiple etches to be performed on a single semiconductor wafer.
Peterson (U.S. Pat. No. 4,599,970) discloses an apparatus for coating a selected area of the surface of an object, wherein a mask is employed for covering portions of the body surface. The mask has openings to expose the exact areas of the object which are to be coated. There is no disclosure of a reactive ion etch chamber for carrying out etching of semiconductor wafers wherein a mechanical mask apparatus or shielding structure is capable of enabling multiple etches at different locations using different processes on a single semiconductor wafer. Moreover, as noted above, a simple mechanical wafer mask has limited use in RIE process development due to the mismatch of materials between the mask and the wafer surface.
Geffcken (U.S. Pat. No. 3,561,993) discloses a method of producing cyclically extending layers, in which similar layers are deposited in a cyclical form through the use of diaphragms forming radial slits therebetween; this arrangement essentially provides; a mask system. The particular mask system as described in this patent is used in material deposition rather than etching, and provides for two moving plates instead of a fixed plate making contact with the object being processed. Thus, although different parts of a wafer may be etched or have material deposited thereon, this disclosure does not utilize a masking or shielding apparatus for a reactive ion etching chamber as contemplated by the present invention.